Fixation sleeve equipped leadless pulse generator

ABSTRACT

A leadless pulse generator is disclosed herein. The leadless pulse generator has a body, a helical anchor, an electrode, and a sleeve. The body includes a distal end and a proximal end opposite the distal end. The helical anchor distally extends from the distal end. The electrode is at the distal end. The sleeve distally extends from the distal end and has a proximal face and a distal face opposite the proximal face. The proximal face is adjacent the body. The sleeve coaxially extends about the helical anchor and further has a biased state wherein the distal face is near a distal tip of the helical anchor. The sleeve is configured to compress such that the distal face displaces proximally towards the proximal face upon the distal face being forced against the cardiac tissue in the course of the helical anchor screwing into the cardiac tissue.

FIELD OF THE INVENTION

Aspects of the present invention relate to medical apparatus andmethods. More specifically, the present disclosure relates to leadlesspulse generators equipped with fixation sleeves. The present disclosurealso relates to methods of manufacturing and using such leadless pulsegenerators.

BACKGROUND OF THE INVENTION

Leadless pulse generators have a helical anchor at a distal end of theleadless pulse generator. The helical anchor is used to secure theleadless pulse generator to cardiac tissue in such a manner that anelectrode of the leadless pulse generator is maintained in appropriatetissue contact for cardiac pacing and sensing.

Since the helical anchor is fixed relative to the rest of the leadlesspulse generator, the leadless pulse generator is rotated as a wholerelative to the cardiac tissue to cause the helical anchor to screw intothe cardiac tissue and thereby fix the leadless pulse generator to thecardiac tissue. Implanters make use of a chevron or other shapedradiopaque marker within the body of the device for visual feedbackunder fluoroscopy when rotating the leadless pulse generator to screwthe helical anchor into the cardiac tissue.

A prescribed number of turns (e.g. 1-¼ turns) of the leadless pulsegenerator is recommended for desirable helical anchor fixation in thecardiac tissue. However, verifying that the prescribed number of turnshas actually resulted in actual turns of the helical anchor screwinginto the cardiac tissue can be a challenge. This challenge results fromthe fact that the leadless pulse generator may be rotated for theprescribed number of turns without the helical anchor fully engaging thecardiac tissue for the entirety of the prescribed number of turns, andthe radiopaque marker viewed via fluoroscopy only conveys to theimplanter that rotation of the leadless pulse generator is occurring,not that the helical anchor is properly screwing into cardiac tissue.

Consequently, there is a need in the art for an improved leadless pulsegenerator configuration and related methods of manufacture and use.

BRIEF SUMMARY OF THE INVENTION

A leadless pulse generator for administering therapy to cardiac tissueis disclosed herein. In one embodiment, the leadless pulse generatorincludes a body, a helical anchor, an electrode, and a sleeve. The bodyincludes a distal end and a proximal end opposite the distal end. Thehelical anchor distally extends from the distal end. The electrode is atthe distal end. The sleeve distally extends from the distal end andincludes a proximal face and a distal face opposite the proximal face.The proximal face is adjacent the body. The sleeve coaxially extendsabout the helical anchor and further includes a biased state wherein thedistal face is near a distal tip of the helical anchor. The sleeve isconfigured to compress such that the distal face displaces proximallytowards the proximal face upon the distal face being forced against thecardiac tissue in the course of the helical anchor screwing into thecardiac tissue. The sleeve may be radiopaque or include a radiopaqueportion or component.

In one embodiment, the leadless pulse generator further includes ananchor mount operably coupled to the distal end and supporting thehelical anchor. A portion of the sleeve is sandwiched between the anchormount and the distal end. The portion of the sleeve may be a radiallyinward extending annular ring. The electrode may be exposed at a centerof the anchor mount, and the anchor mount may be threadably,interference or press fit, swaged, welded, or otherwise operably coupledto the distal end.

In one embodiment, the sleeve includes a proximal section extendingdistally from the proximal face and a distal section extendingproximally from the distal face. The sleeve is configured such that, inthe course of the helical anchor screwing into the cardiac tissue andthe distal face being forced against the cardiac tissue, the distalsection folds proximally and the distal face increases in diameter.

In one embodiment, when the sleeve is in the biased state, the distalsection includes a conical outer shape and the proximal section includesa cylindrical outer shape. The conical outer shape distally increases indiameter. The distal face may change from facing distally to facingradially outward when the distal face displaces proximally towards theproximal face.

In one embodiment, the distal section includes a series oflongitudinally extending gaps and longitudinally extending members. Themembers distally terminate as part of the distal face. The gaps andmembers are arranged in a uniformly spaced alternating fashion about acircumference of the distal section. The members may be wider than thegaps, or the gaps may be wider than the members. The members may changefrom projecting distally to projecting radially outward when the distalface displaces proximally towards the proximal face.

In one embodiment, the sleeve includes a proximal cylindrical sectionextending distally from the proximal face and a distal bellows sectionextending proximally from the distal face. The distal bellows sectionincludes first and second radially outward projecting circumferentiallyextending ridges and a radially inward projecting circumferentiallyextending valley located between the first and second ridges. The sleeveis configured such that, in the course of the helical anchor screwinginto the cardiac tissue and the distal face being forced against thecardiac tissue, the first ridge moves proximally towards the secondridge and the valley decreases in dimension distal-proximal.

A method of manufacturing a leadless pulse generator is also disclosedherein. In one embodiment, the method includes: positioning a distalelectrode of the leadless pulse generator within a hollow interior of acompressible fixation sleeve including at least a radiopaque portion;and coupling the compressible fixation sleeve to the housing of theleadless pulse generator by coupling an anchor mount to the housing suchthat a portion of the compressible fixation sleeve is sandwiched betweenthe anchor mount and a portion of the housing.

The sandwiched portion of the compressible fixation sleeve may be in theform of an inner annular ring. The housing may include a distalprotrusion that boarders the distal electrode and is also positioned inthe hollow interior. The distal protrusion may mechanically couple withthe anchor mount when the anchor mount is coupled to the housing. Forexample, the distal protrusion and the anchor mount may threadablyengage with each other in the course of being mechanically coupled witheach other.

While multiple embodiments are disclosed, still other embodiments of thepresent disclosure will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the disclosure. As will be realized, theinvention is capable of modifications in various aspects, all withoutdeparting from the spirit and scope of the present disclosure.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to thefollowing figures, which are presented as various embodiments of thedisclosure and should not be construed as a complete recitation of thescope of the disclosure, wherein:

FIG. 1 is a diagrammatic depiction of a leadless electrotherapy systemelectrically coupled to a patient heart as viewed from an anterior sideof the patient heart.

FIG. 2A is a side view of a leadless pulse generator that is generallyrepresentative of any of the leadless pulse generators depicted in FIG.1.

FIG. 2B is a distal end view of the leadless pulse generator of FIG. 2A.

FIG. 2C is a side view of the leadless pulse generator as it appears viafluoroscopy and depicting a chevron-shaped rotation direction indicatorthat is part of the leadless pulse generator.

FIG. 3 is a side view of the leadless pulse generator of FIGS. 2-A-2C,except illustrating the leadless pulse generator as being equipped witha compressible radiopaque (or at least partially radiopaque) fixationsleeve.

FIG. 4A is an enlarged side view of the compressible fixation sleeveemployed with the leadless pulse generator of FIG. 3.

FIG. 4B is an end view of the compressible fixation sleeve of FIG. 4A.

FIGS. 5 and 6 are both the same view of the leadless pulse generatordepicted in FIG. 3, except showing the progressive assembly of thesleeve onto the distal end of the leadless pulse generator.

FIGS. 7A and 7B are, respectively, a side elevation and across-sectional elevation of a bellows radiopaque (or at least partiallyradiopaque) compressible fixation sleeve in a non-compressed state aboutan anchor mount and its anchor.

FIGS. 7C and 7D are, respectively, a side elevation and across-sectional elevation of the bellows radiopaque (or at leastpartially radiopaque) compressible fixation sleeve in a compressed stateabout the anchor mount and its anchor.

FIG. 8A is a side elevation of a tubular radiopaque (or at leastpartially radiopaque) compressible fixation sleeve in a non-compressedstate about an anchor mount and its anchor.

FIG. 8B is the same view as FIG. 8A, except showing the tubular sleevein a compressed state about the anchor mount and its anchor.

FIG. 9A is a side elevation of a slit tubular radiopaque (or at leastpartially radiopaque) compressible fixation sleeve in a non-compressedstate about an anchor mount and its anchor.

FIG. 9B is the same view as FIG. 9A, except showing the slit tubularsleeve in a compressed state about the anchor mount and its anchor.

FIG. 10A is a side elevation of a tined tubular radiopaque (or at leastpartially radiopaque) compressible fixation sleeve in a non-compressedstate about an anchor mount and its anchor.

FIG. 10B is the same view as FIG. 10A, except showing the tined tubularsleeve in a compressed state about the anchor mount and its anchor.

DETAILED DESCRIPTION

The present disclosure is directed to a leadless pulse generator 120including a compressible fixation sleeve 130 supported on a distal endof the leadless pulse generator 120, the sleeve 130 coaxially extendingabout a helical anchor 66 distally projecting from the distal end of theleadless pulse generator. At least a portion of the sleeve 130 isradiopaque. The sleeve 130 is configured to bias distally such that thewall structure of the sleeve circumferentially extends about the anchor66 to protect the anchor from engagement with cardiovascular tissue inthe course of tracking to an implantation site in a patient's heart. Thesleeve 130 is configured to proximally compress as a distal face 134 ofthe sleeve 130 abuts against cardiac tissue into which the anchor 66 isbeing screwed, the distal displacement of the distal face 134 relativeto the distal tip of the anchor 66 and/or the proximal face 132 of thesleeve 130 providing information to an implanter via fluoroscopy as towhether or not the anchor 66 is actually screwing into the cardiactissue of the implant site.

In addition to providing an indication of anchoring of the anchor 66into cardiac tissue and protecting against inadvertent tissue damagefrom the anchor while implanting, relocating or retrieving the leadlesspulse generator, the sleeve 130 also provides other benefits. Examplesof such other benefits include providing resistance againstover-rotation of the leadless pulse generator during implant, and awider contact surface to reduce contact pressure and mitigate tissuedamage. Also, the sleeve 130 can form a seal against the endocardium toreduce the possibility of effusion through a potential microperforationcreated by the anchor 66 extending through the thin myocardium. Finally,the compressible sleeve 130 can act to prevent anti-rotation of animplanted leadless pulse generator 120.

Before beginning a discussion regarding the details of the fixationsleeves 130 disclosed herein, a general discussion will first be givenregarding electrotherapy systems employing leadless pulse generators120.

a. Electrotherapy System Employing Leadless Pulse Generator

FIG. 1 is a diagrammatic depiction of a leadless electrotherapy system100 electrically coupled to a patient heart 15 as viewed from ananterior side of the patient heart. The leadless electrotherapy system100 employs one or more leadless pulse generators 120 (e.g., leadlesspacemaker, leadless implantable cardioverter defibrillator(leadless-ICD), or etc.). As discussed in greater detail below, eachleadless pulse generator 120 is substantially enclosed in a hermetichousing suitable for placement on or attachment to the inside or outsideof a cardiac chamber. The leadless pulse generator can have two or moreelectrodes located within, on, or near the housing, for deliveringpacing pulses to muscle of the cardiac chamber and optionally forsensing electrical activity from the muscle, and for bidirectionalcommunication with at least one other device within or outside the body.The housing can contain a primary battery to provide power for pacing,sensing, and communication, for example bidirectional communication. Thehousing can optionally contain circuits for sensing cardiac activityfrom the electrodes. The housing contains circuits for receivinginformation from at least one other device via the electrodes andcontains circuits for generating pacing pulses for delivery via theelectrodes. The housing can optionally contain circuits for transmittinginformation to at least one other device via the electrodes and canoptionally contain circuits for monitoring device health. The housingcontains circuits for controlling these operations in a predeterminedmanner. In alternative embodiments, the housing may contain circuits forreceiving and/or transmitting information via other communication meansincluding, for example, Bluetooth, etc.

In some embodiments, a leadless pulse generator 120 can be adapted forimplantation into tissue in the human body. In a particular embodiment,a leadless cardiac pacemaker can be adapted for implantation adjacent toheart tissue on the inside or outside wall of a cardiac chamber, usingtwo or more electrodes located on or within the housing of thepacemaker, for pacing the cardiac chamber upon receiving a triggeringsignal from at least one other device within the body.

Self-contained or leadless pulse generators are typically fixed to anintracardiac implant site by an actively engaging mechanism such as ascrew or helical member that screws into the myocardium. Examples ofsuch leadless pulse generators are described in the followingpublications, the disclosures of which are incorporated by reference intheir respective entireties herein: (1) U.S. Pat. No. 8,457,742; (2)U.S. Pubiished Application 2007/0088396A1 (now U.S. Pat. No. 9,358,400);(3) U.S. Published Application 2007/0068397A1 (now U.S. Pat. No.9,216,298); (4) U.S. Pat. No. 8,352,025; (5) U.S. Pat. No. 7,937,148;(6) U.S. Pat. No. 7,945,333; (7) U.S. Pat. No. 8,010,209; and (8) Int'lPublication No. W007047681A2.

To begin a more detailed discussion of the features of a leadless pulsegenerator, reference is made to FIGS. 2A and 2B, which are,respectively, a side view and a distal end view of a leadless pulsegenerator 120 as manufactured by St. Jude Medical, Inc. as its NANOSTIM™leadless pacemaker. As can be understood from FIGS. 2A and 2B, theleadless pulse generator 120 can include a hermetic housing 102 with aproximal electrode 104 at a proximal end of the leadless pulse generatorand a distal electrode 112 at a distal end of the leadless pulsegenerator.

As shown in FIGS. 2A and 2B, the distal electrode 112 can be in the formof a distal tip electrode 112. In other embodiments, the distalelectrode 112 can be in the form of a distal ring electrode. In someembodiments, the distal electrode 112 can be integrated within a helicalfixation anchor 66 solely or combined with a distal tip or ringelectrode. The distal electrode 112 and the helical anchor 66 aresupported on the housing 102.

The proximal electrode 104 can be disposed on the housing 102 in theform of a ring electrode 104. The helical fixation anchor 66 can be inthe form of a helically wound wire or other structure capable ofscrewing into tissue for attaching the housing to tissue, such as hearttissue. The helical fixation anchor 66 can be electrically inert in thatit does not act as an electrode. Alternatively, the anchor 66 can beelectrically active wherein the anchor 66 is yet another electrode oracts as an extension of, or part of, the distal electrode 112.

The housing can also include an electronics compartment 110 within thehousing that contains the electronic components necessary for operationof the pulse generator. The hermetic housing 102 can be adapted to beimplanted on or in a human heart, and can be cylindrically shaped,rectangular, spherical, or any other appropriate shape, for example.

The housing 102 can include a conductive, biocompatible, inert, andanodically safe material such as titanium, 316L stainless steel, orother similar materials. The housing can further include an insulatordisposed on the conductive material to separate electrodes 104 and 112.The insulator can be an insulative coating on a portion of the housingbetween the electrodes, and can include materials such as silicone,polyurethane, parylene, or another biocompatible and biostableelectrical insulator commonly used for implantable medical devices. Inone embodiment, a single insulator is disposed along the portion of thehousing between electrodes 104 and 112. In some embodiments, the housingitself can include an insulator instead of a conductor, such as analumina ceramic or other similar materials, and the electrodes can bedisposed upon the housing.

In one embodiment, the leadless pulse generator 120 can include a headerassembly to isolate electrode 104 from electrode 112. The headerassembly can be made from tecothane or another biocompatible plastic,and can contain a ceramic to metal feedthrough, a glass to metalfeedthrough, or other appropriate feedthrough insulator as known in theart.

The electrodes 104 and 112 can include pace/sense electrodes, or returnelectrodes. A low-polarization coating can be applied to the electrodes,such as platinum, platinum-iridium, iridium, iridium-oxide,titanium-nitride, carbon, or other materials commonly used to reducepolarization effects, for example. In FIG. 2A, electrode 112 can be apace/sense electrode and electrode 104 can be a return electrode. Theelectrode 104 can be a portion of the conductive housing 102 that doesnot include an insulator.

As can be understood from FIG. 2A, the leadless pulse generator 120 canalso include a delivery/recovery structure 122 at the extreme proximalend of the leadless pulse generator with which a delivery device (e.g.,delivery catheter) can interface in the implantation or removal of theleadless pulse generator.

As illustrated in FIGS. 2A and 2B, the leadless pulse generator 120 caninclude an anchor mount 131 that is threadably, interference or pressfit, swaged, welded, or otherwise secured to the distal end of thehousing 102 and extends about the distal electrode 112, which distallyprotrudes from a distal end of the anchor mount 131. The helical anchor112 is affixed via mechanical means such as welding, press-fit, or othermeans to the anchor mount 131 such that the anchor mount beingthreadably or otherwise secured to the housing 102 results in the anchor112 being secured to the housing.

As can be understood from FIG. 2C, which is a side view of the leadlesspulse generator as it appears via fluoroscopy, the leadless pulsegenerator 120 can include a chevron-shaped rotation direction indicator124 supported on, or within, the leadless pulse generator. The chevron124 is radiopaque, and implanters can use the chevron shaped radiopaquemarker 124 for visual feedback under fluoroscopy when rotating theleadless pulse generator to screw the helical anchor into the cardiactissue.

Several techniques and structures can be used for attaching the housing102 to the interior or exterior wall of the heart as depicted in FIG. 1.The leadless pulse generator can be delivered endocardially orepicardially through a guiding catheter. A torqueable catheter can beused to rotate the housing and force the helical fixation anchor 66 intoheart tissue, thus affixing the fixation anchor (and also the distalelectrode in FIG. 2A) into contact with stimulatable tissue, asillustrated in FIG. 1. Electrode 104 can serve as an indifferentelectrode for sensing and pacing. The fixation anchor may be coatedpartially or in full for electrical insulation, and a steroid-elutingmatrix may be included on or near the device to minimize fibroticreaction, as is known in conventional pacing electrode-leads. Thehelical fixation anchor 66 may be fixed or extendable/retractablerelative to the distal end of the leadless pulse generator 120.

b. Compressible Radiopaque Fixation Sleeve Distally Extending FromLeadless Pulse Generator Housing And Circumferentially Extending AboutHelical Fixation Anchor

FIG. 3 is a side view of the leadless pulse generator 120 of FIGS.2-A-2C, except illustrating the leadless pulse generator as beingequipped with a compressible radiopaque (or at least partiallyradiopaque) fixation sleeve 130 that extends distally from the housing102 or another portion of the leadless pulse generator 120 andcircumferentially extends about the helical fixation anchor 66 of theleadless pulse generator. The sleeve 130 extends to the distal end ofthe helical anchor 66. During anchor fixation to the endocardium atimplant, the fixation sleeve is intended to compress axially from itsbiased distally projecting state and optionally expand radially whilethe helical anchor 66 within the fixation sleeve 130 screws into cardiactissue.

The fixation sleeve 130 is advantageous for a number of reasons. First,the sleeve 130 protects cardiac tissue and traversed vasculature frompotential trauma as may be caused by interaction with the helical anchor66 during implant, explant and re-positioning.

Second, the fixation sleeve 130 can act as an indicator of tissueengagement. Once the leadless pulse generator 120 begins to rotate andthe anchor tip engages tissue, the fixation sleeve 130 will becompressed as the anchor/tissue engagement increases. Implanters will beable to visually compare the distal edge of the radiopaque fixationsleeve 130 with the helical anchor position and/or the distal end of thepacing electrode 112. Once the radiopaque fixation sleeve 130 iscompressed sufficiently such that the distal edge of the sleeve isaligned with the pacing electrode 112, the implanter can be confidentthat the fixation is fully engaged and the electrode 112 is in contactwith the tissue.

Third and as discussed in detail below, optional anti-rotation featuresof the fixation sleeve 130 can prevent anchor dislodgement once thefixation sleeve is compressed. Since fixation sleeve compression alsoresults in radial expansion, tine features at the end of the expandedfixation sleeve 130 can help resist anti-rotation of the leadless pulsegenerator 120 once helical anchor fixation is achieved.

Fourth, if the helical anchor 66 inadvertently pierces transmurallythrough a very thin region of the atrial or ventricular wall, thefixation sleeve 130 may act as an effective barrier to the effusion ofblood out of the heart and into the pericardial space through thatmicro-perforation.

Finally, the fixation sleeve 130 can be used as a guard againstover-rotation and tissue damage. Sleeve bonding at the base of thefixation sleeve 130, as well as radial expansion of the fixation sleeve,can act as a stop against over-rotation of the leadless pulse generator120 and its potential resulting tissue damage. As the fixation sleeve130 compresses, the surface area against the tissue will grow, therebydecreasing the contact pressure through increased contact surface area.Additional surface area contact will reduce the likelihood of tissuedamage as compared to leadless pulse generators not equipped with thefixation sleeve.

As can be understood from FIGS. 4A and 4B, which are, respectively,enlarged side and end views of the fixation sleeve 130 employed with theleadless pulse generator 120 of FIG. 3, the sleeve 130 includes aproximal face 132 and a distal face 134 opposite the proximal face. Anexterior proximal cylindrical section 136 extends distally from theproximal face to an exterior transition 138 to an exterior distalconical section 140 that extends distally from the exterior transition138 to the distal face 134, which has a diameter that is greater than adiameter of the proximal face 132. Thus, the exterior distal conicalsection 140 provides the sleeve 130 with a distally flared exterior ascompared to the cylindrical exterior of the exterior proximal section136.

The sleeve 130 includes a hollow interior 142 which is defined by aseries of internal surfaces including an internal proximally expandingconical section 144 distally extending from the proximal face 132 to aninner annular ring 146. An interior intermediate cylindrical section 148extends distally from the annular ring 146 to an interior transition150. An interior distally expanding conical section 152 extends distallyfrom the interior transition 150 to the distal face 134. The annularring 146 includes a proximal surface 154, a cylindrical inner surface156 and a distal surface 158. The proximal and distal surfaces 154, 158extend radially inward from the adjacent internal surfaces of the wallstructure of the sleeve 130. The conical arrangements of the sleeve 130depicted in FIGS. 4A and 4B work together to facilitate the sleevefolding back on itself as the helical anchor 66 screws increasinglydeeper into cardiac tissue abutting against the distal face 134 of thesleeve 130.

While the embodiment depicted in FIGS. 4A and 4B is described as havingan exterior distal conical section 140 and an interior distal conicalsection 152, in other embodiments, these two distal conical sections140, 152 may be simply cylindrical such that the two distal sections140, 152 simply extend from their immediately adjacent proximalsections, the sleeve thereby having and overall cylindrical inner andouter shape over its entirety distal the annular ring 146.

In one embodiment, the sleeve 130 is made of a low-durometer medicalgrade polymeric material such as a liquid silicone rubber (LSR)elastomer urethane, expanded polytetrafluoroethylene (EPTFE), or mostany biocompatible soft thermoplastic, biocompatible textile, orbiocompatible woven composite, wherein any of the aforementionedmaterials form the sleeve 130 and a radiopaque additive such asplatinum, platinum-iridium alloy, tantalum, tungsten, TiO₂, BaSO₄, oretc. is added throughout the sleeve. Alternatively, in one embodiment,the radiopaque additive could be restricted to a subsection of thesleeve such as the distal section 140 or extreme distal edge of thesleeve 130. In one embodiment, the sleeve may have a radiopaque markerin the form of a ring, beads or ring segments extending along a distalcircumference or extreme distal circumferential edge of the sleeve 130.In such an embodiment, the radiopaque ring, beads or ring segments maybe inserts molded into the sleeve, the inserts being in the form of aradiopaque material such as platinum, platinum-iridium alloy, tantalum,tungsten, TiO₂, BaSO₄, or etc.

To discuss the assembly of the sleeve 130 onto the distal end of theleadless pulse generator 120, reference is made to FIGS. 5 and 6, whichare both the same view of the leadless pulse generator 120 depicted inFIG. 3, except showing the progressive assembly of the sleeve onto thedistal end of the leadless pulse generator. As shown in FIG. 5, theanchor mount 131 and helical anchor 66 are absent from the distal end ofthe leadless pulse generator 120, revealing a threaded distal protrusion160 of the housing 102, the protrusion 160 extending circumferentiallyabout the distal electrode 112. To begin the assembly, the sleeve 130 iscoaxially aligned with the longitudinal axis of the leadless pulsegenerator with the proximal face 132 of the sheath 130 facing the distalend of the leadless pulse generator 130 and the distal face 134 of thesheath 130 facing away from the leadless pulse generator.

As shown in FIG. 6 and with reference to FIGS. 4A, 4B and 5, the sleeve130 is then seated against the distal end of the leadless pulsegenerator 120 such that the threaded distal protrusion 160 and electrode112 extend through the hollow interior 142 of the sleeve 130, theproximal conical surface 144 of the sleeve matingly abutting against acomplementary conical surface of the distal end of the housing 102, theproximal surface 154 of the inner annular ring 146 of the sleeveabutting against a distal face of the distal end of the housing 102, andthe cylindrical inner surface 156 of the annular ring 146 of the sleeve130 making circumferential surface contact with an outer cylindricalsurface of the threaded distal protrusion 160 of the housing 102.

As depicted in FIG. 3 and with reference to FIGS. 4A-6, the sleeve 130is then secured in place by the anchor mount 131 being threaded orotherwise secured on the distal protrusion 160 of the housing 102 suchthat the inner annular ring 146 is sandwiched between a proximal end ofthe anchor mount and the distal end of the housing 102.

In some embodiments, the compressible radiopaque (or at least partiallyradiopaque) fixation sleeve 130 will have configurations different thanthat depicted in FIGS. 3-6, but will still employ an inner annular ring146 that is sandwiched between the anchor mount 131 and the housing 102for securing the sleeve 130 to the housing 102. For example and asdiscussed in detail below, the sleeve 130 may have a bellowsconfiguration (see FIGS. 7A-7D), a tubular configuration (see FIGS. 8Aand 8B), a slit tubular configuration (see FIGS. 9A and 9B), and a tineconfiguration (see FIGS. 10A and 10B). Each of the configurations willnow be discussed in turn.

FIGS. 7A-7D illustrate the bellows sleeve 130, wherein FIGS. 7A and 7Bare, respectively, a side elevation and a cross-sectional elevation ofthe bellows radiopaque (or at least partially radiopaque) compressiblefixation sleeve in a non-compressed state (i.e., its biased state) aboutan anchor mount 131 and its anchor 66, and FIGS. 7C and 7D are,respectively, the same views, except showing the bellows sleeve 130 in acompressed state about the anchor mount 131 and its anchor 66. As can beunderstood from FIGS. 7A and 7B, the sidewall of the bellows sleeve 130extends in a serpentine fashion between the proximal face 132 and thedistal face 134 of the sleeve 130. The wall structure of the sleeve 130includes a cylindrical section 170 extending distally from the proximalface 132 to the proximal boundary of a bellows structure 171 of thesleeve 130. Although not illustrated in FIGS. 7A-7D, in one embodiment,the inner annular ring 146 discussed above with respect to FIGS. 4A and4B may be similarly locate in the cylindrical section 170 of the bellowssleeve 130 depicted in FIGS. 7A-7D for purposes of securing the bellowssleeve 130 to the housing 102 of the leadless pulse generator in amanner as discussed with respect to FIGS. 3-6 above.

Referring to FIGS. 7A and 7B and continuing proximal to distal along thebellows structure 171 from the cylindrical section 170, the bellowsstructure 171 proximally begins with a first arcuate radially outwardprojecting and circumferentially extending ridge 172. The first ridge172 transitions into an arcuate radially inward projecting andcircumferentially extending valley 174. The valley 174 transitions intoa second arcuate radially outward projecting and circumferentiallyextending ridge 176 that transitions into a distal ringed terminus 178of the sleeve 130, the distal edge of the distal ringed terminus 178 ofthe sleeve 130 forming the distal face 134 of the sleeve 130. The distalringed terminus 178 may have a circular cross-section. In oneembodiment, the distal ringed terminus 178 may be made of a radiopaquepliable polymer material or be a radiopaque ring imbedded in the pliablepolymer material forming the rest of the sleeve 130

When the bellows sleeve 130 is compressed from the non-compressed stateof FIGS. 7A and 7B to the compressed state of FIGS. 7C and 7D, thebellows structure 171 compresses proximal-distal, its first and secondridges 172, 176 abutting together on account of the valley 174 havingcollapsed radially inward and proximal-distal. Thus, while the helicalanchor 66 is hidden within the circumferential confines of the bellowssleeve 130 when the sleeve 130 is in the non-compressed state depictedin FIGS. 7A and 7B, a distal region of the helical anchor 66 is exposedwhen the sleeve 130 is in the compressed state depicted in FIGS. 7C and7D on account of the distal face 134 having been compressed proximallycloser to the proximal face 132.

FIGS. 8A and 8B illustrate the tubular sleeve 130, wherein FIG. 8A is aside elevation of a tubular radiopaque (or at least partiallyradiopaque) compressible fixation sleeve in a non-compressed state(i.e., its biased state) about an anchor mount 131 and its anchor 66,and FIG. 8B is the same view, except showing the tubular sleeve 130 in acompressed state about the anchor mount 131 and its anchor 66. As can beunderstood from FIG. 8A, the sidewall of the tubular sleeve 130 extendsin a generally tubular or cylindrical fashion moving distally from theproximal face 132 until the wall structure of the sleeve radially flairsoutward in a generally conical fashion a distal third of the sleeve 130distally ending at the distal face 134 of the sleeve 130. Thus, the wallstructure of the sleeve 130 includes a proximal cylindrical section 170extending distally from the proximal face 132 to the proximal boundaryof a distal conical section 140 of the sleeve 130. The distal conicalsection 140 distally transitions into a distal ringed terminus 178 ofthe sleeve 130. The distal edge of the distal ringed terminus 178 of thesleeve 130 forms the distal face 134 of the sleeve 130. The distalringed terminus 178 may have a circular cross-section.

Although not illustrated in FIGS. 8A and 8B, in one embodiment, theinner annular ring 146 discussed above with respect to FIGS. 4A and 4Bmay be similarly locate in the cylindrical section 170 of the tubularsleeve 130 depicted in FIGS. 8A and 8B for purposes of securing thetubular sleeve 130 to the housing 102 of the leadless pulse generator ina manner as discussed with respect to FIGS. 3-6 above.

When the tubular sleeve 130 is compressed from the non-compressed stateof FIG. 8A to the compressed state of FIG. 8B, the distal conicalsection 140 proximally folds back on itself and radially outwardlyexpands in diameter. Thus, while the helical anchor 66 is hidden withinthe circumferential confines of the tubular sleeve 130 when the sleeve130 is in the non-compressed state depicted in FIG. 8A, a distal regionof the helical anchor 66 is exposed when the sleeve 130 is in thecompressed state depicted in FIG. 8B on account of the distal face 134having been compressed proximally closer to the proximal face 132.

As can be understood from a comparison of FIGS. 8A and 8B, the sleeve130 is configured such that, in the course of the helical anchor 66screwing into the cardiac tissue and the distal face 134 being forcedagainst the cardiac tissue, thereby transitioning the sleeve 130 fromits biased state (FIG. 8A) to its deflected state (FIG. 8B), the distalsection 140 folds proximally and the distal face 134 increases indiameter. Also, the distal face 134 changes from facing distally tofacing radially outward when the distal face 134 displaces proximallytowards the proximal face 132.

FIGS. 9A and 9B illustrate the slit tubular sleeve 130, wherein FIG. 9Ais a side elevation of a slit tubular radiopaque (or at least partiallyradiopaque) compressible fixation sleeve in a non-compressed state(i.e., its biased state) about an anchor mount 131 and its anchor 66,and FIG. 9B is the same view, except showing the slit tubular sleeve 130in a compressed state about the anchor mount 131 and its anchor 66.

As can be understood from a comparison of the tubular embodimentdepicted in FIGS. 8A and 8B to the slit tubular embodiment of FIGS. 9Aand 9B, the two embodiments are substantially similar, except the distalconical region 140 of the slit tubular embodiment of FIGS. 9A and 9Bincludes a series of relatively narrow gaps 200 defined in the distalconical section 140 of the slit tubular embodiment of FIGS. 9A and 9B.Specifically, the distal conical section 140 of the slit tubularembodiment of FIGS. 9A and 9B includes a series of longitudinallyextending slits or slots 200 extending the length of the distal conicalsection 140, and these slits 200 are evenly distributed about thecircumference of the distal conical section 140. The slits 200 may berectangular shaped or any other shape. The slits 200 define a series oflongitudinally extending readily pliable members 202 that are evenlydistributed about the circumference of the distal conical section 140.The members 202 may be rectangular shaped or any other shape.

Although not illustrated in FIGS. 9A and 9B, in one embodiment, theinner annular ring 146 discussed above with respect to FIGS. 4A and 4Bmay be similarly locate in the cylindrical section 170 of the slittubular sleeve 130 depicted in FIGS. 9A and 9B for purposes of securingthe slit tubular sleeve 130 to the housing 102 of the leadless pulsegenerator in a manner as discussed with respect to FIGS. 3-6 above.

When the slit tubular sleeve 130 is compressed from the non-compressedstate of FIG. 9A to the compressed state of FIG. 9B, the members 202 ofthe distal conical section 140 proximally fold back on themselves andradially outwardly splay in an increased diameter. Thus, while thehelical anchor 66 is hidden within the circumferential confines of theslit tubular sleeve 130 when the sleeve 130 is in the non-compressedstate depicted in FIG. 9A, a distal region of the helical anchor 66 isexposed when the sleeve 130 is in the compressed state depicted in FIG.9B on account of the distal face 134 having been compressed proximallycloser to the proximal face 132.

As can be understood from a comparison of FIGS. 9A and 9B, the sleeve130 is configured such that, in the course of the helical anchor 66screwing into the cardiac tissue and the distal face 134 being forcedagainst the cardiac tissue, thereby transitioning the sleeve 130 fromits biased state (FIG. 9A) to its deflected state (FIG. 9B), the distalsection 140 folds proximally and the distal face 134 increases indiameter. Also, the distal face 134 changes from facing distally tofacing radially outward when the distal face 134 displaces proximallytowards the proximal face 132, Further, the members 202 change fromprojecting distally to projecting radially outward when the distal face134 displaces proximally towards the proximal face 132.

As can be understood from a comparison of the slit tubular embodimentdepicted in FIGS. 9A and 9B to the tined tubular embodiment of FIGS. 10Aand 10B, the two embodiments are substantially similar, except the slittubular embodiment of FIGS. 9A and 9B includes a series of relativelynarrow gaps 200 and a series of relatively wide members 202 while thetined tubular embodiment includes a series of relatively wide gaps 200and a series of relatively narrow pliable members 202 that may beconsidered pliable tines 202. Specifically, the distal conical section140 of the tined tubular embodiment of FIGS. 10A and 10B includes aseries of longitudinally extending slits or slots 200 extending thelength of the distal conical section 140, and these slits 200 are evenlydistributed about the circumference of the distal conical section 140.The slits 200 may be rectangular shaped or any other shape. The slits200 define a series of longitudinally extending readily pliable membersor tines 202 that are evenly distributed about the circumference of thedistal conical section 140. The members 202 may be rectangular shaped orany other shape.

Although not illustrated in FIGS. 10A and 10B, in one embodiment, theinner annular ring 146 discussed above with respect to FIGS. 4A and 4Bmay be similarly locate in the cylindrical section 170 of the tinedtubular sleeve 130 depicted in FIGS. 10A and 10B for purposes ofsecuring the tined tubular sleeve 130 to the housing 102 of the leadlesspulse generator in a manner as discussed with respect to FIGS. 3-6above.

When the tined tubular sleeve 130 is compressed from the non-compressedstate (i.e., its biased state) of FIG. 10A to the compressed state ofFIG. 10B, the members or tines 202 of the distal conical section 140proximally fold back on themselves and radially outwardly splay in anincreased diameter. Thus, while the helical anchor 66 is hidden withinthe circumferential confines of the tined tubular sleeve 130 when thesleeve 130 is in the non-compressed state depicted in FIG. 10A, a distalregion of the helical anchor 66 is exposed when the sleeve 130 is in thecompressed state depicted in FIG. 10B on account of the distal face 134having been compressed proximally closer to the proximal face 132.

As can be understood from a comparison of FIGS. 10A and 10B, the sleeve130 is configured such that, in the course of the helical anchor 66screwing into the cardiac tissue and the distal face 134 being forcedagainst the cardiac tissue, thereby transitioning the sleeve 130 fromits biased state (FIG. 10A) to its deflected state (FIG. 10B), thedistal section 140 folds proximally and the distal face 134 increases indiameter. Also, the distal face 134 changes from facing distally tofacing radially outward when the distal face 134 displaces proximallytowards the proximal face 132. Further, the members 202 change fromprojecting distally to projecting radially outward when the distal face134 displaces proximally towards the proximal face 132.

The following discussion pertains to a delivery method for implanting aleadless pulse generator 120 equipped with a fixation sleeve 130 such asany of those disclosed herein. The method begins with the leadless pulsegenerator 120 being tracked via delivery tools (e.g., a deliverycatheter, etc.) through the patient vasculature to an implantation sitein the patient's heart. Upon the distal end of the leadless pulsegenerator being placed against the implantation site, gentle forwardpressure is applied on the delivery catheter until noticing a slightmovement of the delivery catheter proximal to the leadless pulsegenerator and synchronous to the heartbeat. The curve of the catheterdown to the inferior vena cava is visualized via fluoroscopy. Theimplant site and the distal region of the delivery tool(s), plus theleadless pulse generator 120 and its fixation sleeve 130, are visualizedvia fluoroscopy while the leadless pulse generator 120 is caused torotate clockwise as the radiopaque marker 124 of the leadless pulsegenerator is observed, its turns being counted for the appropriatenumber of turns to cause the helical anchor 66 to screw fully into thecardiac tissue. Simultaneously, the distal face 134 of the radiopaquefixation sleeve 130 and the helical anchor 66 are observed viafluoroscopy, including the positional relationship of the distal face134 of the sleeve 130 relative to the anchor 66.

While visualizing the radiopaque fixation sleeve during the rotation ofthe leadless pulse generator 120, if the distal tip electrode 112remains proximal to the distal face 134 of the fixation sleeve 130, theimplanter can safely continue rotating the leadless pulse generatoruntil alignment is observed. Once the helical anchor 66 is adequatelyimbedded in the cardiac tissue, as can be understood from therelationship of the distal face 134 of the fixation sleeve 130 relativeto the distal tip electrode 112 and/or the helical anchor 66, theimplanter can uncouple the leadless pulse generator 120 from thedelivery tool(s) with confidence that the leadless pulse generator 120is securely anchored to the engaged cardiac tissue.

As noted above, the fixation sleeve equipped leadless pulse generator120 disclosed herein is advantageous for a number of reasons. First, theprotective sleeve 130 prevents helical anchor engagement or deformationdue to inadvertent snagging of cardiac tissue. Second, the compressiblesleeve 130 allows fluoroscopic evaluation of distance between cardiactissue and the distal end electrode 112, thereby conveying informationto the implanter regarding whether or not the anchor 66 is properlyscrewing into cardiac tissue and to what extent. Third, the compressiblesleeve 130 provides resistance against over-rotation of the leadlesspulse generator during implant. Fourth, the compressible sleeve 130provides additional contact surface area to reduce contact pressure andmitigate tissue damage. Fifth, the compressible sleeve forms a sealagainst the endocardium to reduce the possibility of effusion throughany potential microperforation created by the helical anchor 66extending through the thin myocardium. Finally, the compressible sleeve130 with tines or other radially splaying members 202 can act to preventanti-rotation of an implanted leadless pulse generator 120.

The foregoing merely illustrates the principles of the invention.Various modifications and alterations to the described embodiments willbe apparent to those skilled in the art in view of the teachings herein.It will thus be appreciated that those skilled in the art will be ableto devise numerous systems, arrangements and methods which, although notexplicitly shown or described herein, embody the principles of theinvention and are thus within the spirit and scope of the presentinvention. From the above description and drawings, it will beunderstood by those of ordinary skill in the art that the particularembodiments shown and described are for purposes of illustrations onlyand are not intended to limit the scope of the present invention.References to details of particular embodiments are not intended tolimit the scope of the invention.

What is claimed is:
 1. A leadless pulse generator for administeringtherapy to cardiac tissue, the leadless pulse generator comprising: abody having a distal end and a proximal end opposite the distal end; ahelical anchor distally extending from the distal end; an electrode atthe distal end; and a sleeve coupled to the body and distally extendingfrom the distal end of the body, the sleeve comprising a proximal faceand a distal face opposite the proximal face, the proximal face adjacentthe body, the sleeve coaxially extending about the helical anchor, thesleeve configurable in a biased state wherein the distal face is near adistal tip of the helical anchor, the sleeve configured to compress suchthat the distal face displaces proximally towards the proximal face uponthe distal face being forced against the cardiac tissue in the course ofthe helical anchor screwing into the cardiac tissue.
 2. The leadlesspulse generator of claim 1, further comprising an anchor mount operablycoupled to the distal end and supporting the helical anchor, and aportion of the sleeve is sandwiched between the anchor mount and thedistal end.
 3. The leadless pulse generator of claim 2, wherein theportion of the sleeve is a radially inward extending annular ring. 4.The leadless pulse generator of claim 2, wherein the electrode isexposed at a center of the anchor mount.
 5. The leadless pulse generatorof claim 2, wherein the anchor mount is threadably operably coupled tothe distal end.
 6. The leadless pulse generator of claim 1, wherein thesleeve is radiopaque or comprises a radiopaque portion or component. 7.The leadless pulse generator of claim 1, wherein the sleeve has aproximal section extending distally from the proximal face and a distalsection extending proximally from the distal face, the sleeve configuredsuch that, in the course of the helical anchor screwing into the cardiactissue and the distal face being forced against the cardiac tissue, thedistal section folds proximally and the distal face increases indiameter.
 8. The leadless pulse generator of claim 7, wherein, when thesleeve is in the biased state, the distal section has a conical outershape and the proximal section has a cylindrical outer shape, theconical outer shape distally increasing in diameter.
 9. The leadlesspulse generator of claim 7 wherein the distal section further comprisesa series of longitudinally extending gaps and longitudinally extendingmembers, the members distally terminating as part of the distal face,the gaps and members arranged in a uniformly spaced alternating fashionabout a circumference of the distal section.
 10. The leadless pulsegenerator of claim 9, wherein the members are wider than the gaps. 11.The leadless pulse generator of claim 9, wherein the gaps are wider thanthe members.
 12. The leadless pulse generator of claim 9, wherein themembers change from projecting distally to projecting radially outwardwhen the distal face displaces proximally towards the proximal face. 13.The leadless pulse generator of claim 1, wherein the distal face changesfrom facing distally to facing radially outward when the distal facedisplaces proximally towards the proximal face.
 14. The leadless pulsegenerator of claim 1, wherein the sleeve has a proximal cylindricalsection extending distally from the proximal face and a distal bellowssection extending proximally from the distal face, the distal bellowssection having first and second radially outward projectingcircumferentially extending ridges and a radially inward projectingcircumferentially extending valley located between the first and secondridges.
 15. The leadless pulse generator of claim 11, wherein the sleeveis configured such that, in the course of the helical anchor screwinginto the cardiac tissue and the distal face being forced against thecardiac tissue, the first ridge moves proximally towards the secondridge and the valley decreases in dimension distal-proximal.
 16. Theleadless pulse generator of claim 1 wherein the helical anchor also actsas part of the electrode or is another electrode.